The present invention relates generally to methods of surface treating a metal article, such as polishing a metal surface. The present invention has particular applicability in chemical mechanical polishing (CMP) of non-magnetic substrates for use in manufacturing high area 1 density magnetic recording media exhibiting low noise and high coercivity.
Various metal platings, such as nickel (Ni) platings or deposits, enjoy technological applicability in various industries, such as the electronic, oil and gas, aerospace, machinery, automobile and magnetic recording media industries. For example, electroless Ni is employed in the metal finishing industry for various metal substrates, including steel, copper, aluminum and alloys thereof. Conventional electrolessly deposited Nixe2x80x94P platings exhibit desirable physical and chemical properties, such as hardness, lubricity, appearance, and corrosion resistance. An amorphous Nixe2x80x94P plating is conventionally applied to a non-magnetic substrate, such as an aluminum (Al) or an Al-alloy substrate in manufacturing magnetic recording media.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Increasing speed and capacity requirements are forcing disk drives to become smaller and the flying height of the head to be even closer to the recording medium. At ever increasingly small distances, both the head and the disk must be very flat. Thus, the material used for the disk should be very stiff and amenable to a fine finish.
A typical longitudinal recording medium comprises a non-magnetic substrate, typically made of an aluminum (Al)-alloy, such as an aluminum-magnesium (Alxe2x80x94Mg)-alloy, plated with a continuous layer of amorphous nickel-phosphorus (NiP) substantially over the substrate. In completing the fabrication of a magnetic disk, a magnetic layer is typically sequentially deposited on each side of the nickel alloy. A protective overcoat layer and a lubricant topcoat are typically sequentially formed on the magnetic layer to complete the fabrication of the magnetic recording medium.
To provide the current smoothness required for a high areal density magnetic recording media exhibiting low noise and high coercivity, various layers on the substrate require polishing. For example, a polished Nixe2x80x94P plating increases the hardness of the Al substrate, and serves as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
Conventional techniques for treating various metal surfaces, such as Al, Ni and Nixe2x80x94P, include CMP for polishing and smoothening the surface of the metal. In conventional CMP techniques, a carrier assembly is rotated in contact with a polishing pad in a CMP apparatus. The polishing pad is mounted on a rotating turntable or platen, or moving above a stationary polishing table, driven by an external driving force. The metal coated substrates are typically mounted on the carrier or polishing head which provides a controllable pressure urging the substrate against the rotating polishing pad. Thus, the CMP apparatus effects polishing or rubbing movement between the substrate and the polishing pad while dispersing a polishing slurry, typically containing abrasive particles in a reactive solution typically comprising an oxidizer, to effect both chemical activity and mechanical activity while applying a force between the substrate and a polishing pad.
It is, however, extremely difficult to smoothen a hardened non-magnetic substrate without encountering severe surface defects, such as surface roughness, scratches and pitting. These surface defects are virtually impossible to recover without the expenditure of an inordinate, prohibitive amount of polishing time. Conventional smoothening methodology, therefore, cannot provide a non-magnetic substrate with a hardened surface having an average surface roughness (Ra) less than 4 xc3x85 to 5 xc3x85.
Accordingly, a continuing need exists a for methodology enabling surface treatment, such as CMP, of metal surfaces with reduced defects and enhanced production throughput. There exists a particular need for methodology enabling the manufacture of magnetic recording media comprising a non-magnetic substrate having a smoothened surface.
An advantage of the present invention is an efficient method for surface treating a metal with reduced surface defects.
Another advantage of the present invention is a method of manufacturing a magnetic recording media comprising CMP the surface of a non-magnetic substrate with reduced surface defects and enhanced production throughput.
According to the present invention, the foregoing and other advantages achieved by a method of polishing a substrate having a metal surface. The method includes polishing a non-magnetic, metal coating, such as a nickel or nickel alloy, on a substrate suitable for the production of a magnetic recording medium. The method comprises: polishing a surface of the metal on the substrate with a colloidal slurry to reduce surface roughness; collecting the colloidal slurry used in polishing the surface of the metal; and combining unused colloidal slurry with the collected colloidal slurry to form a mixed slurry.
Embodiments of the present invention include polishing the surface of the metal on the substrate to a predetermined roughness with a non-colloidal polishing slurry prior to polishing the surface of the metal on the substrate with the colloidal slurry; collecting the colloidal slurry in a collection tank; separating the colloidal slurry from any settled metal residue and then adding the unused colloidal slurry to the separated colloidal slurry to form the mixed slurry and using the mixed slurry to polish additional metal surfaces.
The colloidal slurry of the present invention comprises an abrasive, with or without additional agents, dispersed in a medium. In an embodiment of the present invention, the colloidal slurry comprises abrasive particles having an average size of less than 1 micron dispersed in an aqueous medium with an oxidizing agent.
Another aspect of the present invention is a method of polishing substrates having a metal surface, the method comprising: polishing a first metal surface on a first substrate with a colloidal slurry to reduce surface roughness on the first metal surface of the first substrate; collecting the colloidal slurry used in polishing the first metal surface of the first substrate; and polishing a second substrate having a second metal surface with the collected colloidal slurry to reduce surface roughness on the second metal surface of the second substrate.
Embodiments include polishing both first and second metal surfaces each for about several seconds to about several minutes with the colloidal slurry and a CMP pad to an average surface roughness (Ra) of about 1.5 xc3x85 to about 3 xc3x85; rinsing the polished surfaces with water; and drying the polished surfaces. A magnetic recording medium can then be fabricated from the polished substrate by forming a magnetic layer on the polished metal surface; forming a protective overcoat on the magnetic layer; and forming a lubricant topcoat on the protective overcoat.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the description is to be regarded as illustrative in nature, and not as restrictive.